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Understanding the effects of mixed anthropogenic pollutants on the photooxidation of volatile organic compounds (VOCs) is essential for unraveling the formation pathways of secondary organic aerosols (SOA). Yet, it remains a highly challenging experimental target owing to the complexities in the precise measurement of molecular compositions of products and number/mass concentrations of particles as a function of pollutant concentration in the ambient atmosphere. Here, a series of well-defined chamber experiments were performed to explore the effects of NO x and NH 3 on the SOA formation from photooxidation of the most abundant monoterpene, α -pinene. The results indicate that the suppression effect of NO and NO 2 on the α -pinene photooxidation shows monotonous and parabolic trends, respectively. The presence of NH 3 enhances particle number concentrations during the α -pinene + NO x photooxidation by participating in reactions with organic acids. New compounds, including organic peroxides, esters, organic nitrates, and peroxyacyl nitrates, are observed at molecular weight (MW) = 166, 173, 217, 231, 280, 282, 304, and 410 through threshold photoionization making use of a recently constructed vacuum ultraviolet free electron laser in positive ion mode. The molecular structures and formation paths of these species are speculated, which advance the category of VOC oxidation products. Our study provides significant understanding of the influence of NO x and NH 3 on the VOC photooxidation, which can be utilized to establish predictive SOA formation networks and to improve atmospheric models. [Display omitted] • This study investigates the atmospheric components affected by the anthropogenic-biogenic interactions. • The suppression effect of NO and NO 2 on the α -pinene photooxidation shows monotonous and parabolic trends, respectively. • NH 3 enhances the number concentrations of SOA from the α -pinene + NO x photooxidation by reacting with organic acids. • A series of newly-observed compounds advance understanding of atmospheric components. [ABSTRACT FROM AUTHOR]

Biogenic volatile organic compounds (BVOCs) are the largest source of secondary organic aerosols (SOA) globally. However, the complex interactions between marine and terrestrial BVOCs remain unclear, inhibiting our in-depth understanding of the SOA formation in the coastal areas and its environmental impacts. Here, we performed smog chamber experiments with mixed α -pinene (a typical monoterpene) and dimethyl sulfide (DMS, a typical marine emission BVOC) to investigate their possible interactions and subsequent SOA formation. It is found that DMS has a non-linear effect on SOA generation: The mass concentration and yield of SOA show increasing and then decreasing trends with the increase of the initial concentration of DMS. The increasing trend can be attributed to OH regeneration from isomerization of the CH 3 SCH 2 OO radical together with acid-catalyzed heterogeneous reactions by the oxidation of DMS, while the decreasing trend is explained by the less contribution of isomerization reaction and the high OH reactivity that inhibits the formation of low volatility products. The results from infrared spectra and mass spectra together reveal the contribution of sulfur-containing molecules in the mixed system. Moreover, the mass spectra results indicate that acidic products generated by DMS photooxidation enhance the O:C ratio, while organosulfates are produced to contribute to the formation of mixed SOA. In addition, the trends in relative abundance of highly oxygenated organic molecules (HOMs) with C 8 - C 10 multiple functional groups in different mixed systems agree well with the turning point of the SOA yield. The findings of this study have significant implications for understanding binary or more complex systems in the atmosphere in the coastal areas. [Display omitted] • Nonlinear effect of DMS on the generation of α -pinene SOA in mixed systems. • OH regeneration and acid catalysis dominate the generation of mixed SOA. • OH reactivity inhibits the formation of low-volatility intermediates. • DMS affects the composition by contributing to the formation of OS and HOMs. [ABSTRACT FROM AUTHOR]

Biogenic secondary organic aerosols (BSOA) play a crucial role in atmospheric chemistry, with significant implications for air quality and human health. However, the mechanisms by which anthropogenic emissions influence the formation of BSOA in the real atmosphere have not been fully understood. In this study, fine aerosol (PM 2.5) samples were collected during both the wet and dry seasons at a high-altitude (1690 m) background site in the Nanling Mountains. Eleven typical secondary organic aerosols (SOA) tracers derived from isoprene (SOA I), α/β-pinene (SOA M), β-caryophyllene (SOA S), and toluene (SOA A), as well as water-soluble inorganic ions and the ambient concentrations of isoprene and its two primary oxidation products, were measured. The results showed that the concentrations and composition of SOA tracers exhibited significant seasonal variations. The total concentration of SOA tracers in the wet season (159 ± 100 ng m−3) was almost three times higher than that in the dry season (61 ± 68 ng m−3). SOA I dominated in both seasons, followed by SOA M , SOA S , and SOA A. Compared with other studies, the concentrations of SOA I and SOA A in the wet season were relatively high, which was mainly attributed to the rapid oxidation of their precursors due to the higher atmospheric oxidative capacity. C 5 -alkene triols had a significantly higher proportion in SOA I species than in other mountaintop sites. Temperature was the main factor causing the seasonal difference in the concentration of SOA I. Anthropogenic pollutants significantly promoted the formation of SOA I in the wet season. The influence of anthropogenic pollutants on the reaction pathway of IEPOX was consistent in both seasons, favoring the formation of C 5 -alkene triols. Our study provides vital insights into the molecular characteristics and formation mechanisms of BSOA in a high-altitude background region. It also highlights that the complex air pollution not only affects BSOA concentrations but also the reaction pathways of biogenic volatile organic compounds (BVOCs) transforming into BSOA. • BSOA tracers were firstly measured in Nanling Mountains. • Quick oxidation of locally emitted isoprene was the main contributor to isoprene SOA. • Strong atmospheric oxidation capacity in Mt. Nanling was evidenced by low isoprene and high SOA tracer levels. • In the wet season, anthropogenic pollutants markedly enhanced isoprene SOA formation. • C5-alkene triols were more prevalent in isoprene SOA tracers at our site than at other mountaintops. [ABSTRACT FROM AUTHOR]

We propose the use of thermal-desorption dichloromethane-induced low-pressure photoionization mass spectrometry (TD-CH 2 Cl 2 -induced LPPI-MS) via a laboratory-built krypton vacuum ultraviolet lamp for the real-time analysis of α-pinene secondary organic aerosol (αP-SOA). Using this technology, the peak intensities of the majority of SOA were enhanced by at least two orders of magnitude after doping with 720 ppm dichloromethane. Clear temporal evolutions of the SOA oxidation products with particle formation were also observed. The molecular ion peaks at m/z value of 153 and 109 showed a similar sharp increase with particle-number concentration. These two species (i.e. protonated α-campholenic aldehyde or dehydrated protonated pinalic-3-acid) with the fragment at m/z 153 and 109 may be critical species to prompt new particle formation. Furthermore, the monomers with the fragment ion peaks at m/z value of 69 and 87 (i.e. protonated pinonic acid, pinic acid, oxopinonic acid, and OH-pinonic acid etc.) were found to be intermediate species with high reactivities during SOA growth. The obtained results provide supplementary knowledge regarding the characterization and temporal evolution of the key components that promote αP-SOA formation. Image 1 • α-Pinene SOA was on-line monitored with TD-CH 2 Cl 2 -Induced LPPI-MS. • Species with with m/z 153 and 109 fragments mainly prompt NPF. • Intermediate species with the m/z 69 and 87 fragments mainly prompt SOA growth. • Formation mechanisms of newly fragment species were proposed. [ABSTRACT FROM AUTHOR]

The detailed molecular composition of laboratory-generated secondary organic aerosols (SOA) during the high-NO photooxidation of β-pinene (βP) was investigated using a novel thermal desorption dichloromethane-assisted low-pressure photoionization mass spectrometry (TD-CH 2 Cl 2 -assisted LPPI-MS) technique. We found that protonated norpinone gave the highest signal intensity, which supported that assumption that this compound was the key oxidation species responsible for promoting βP-SOA formation. In addition to the previously identified monomers (i.e., 2,2-dimethylcyclobutyl-1,3-dicarboxaldehyde (m/z 140), pinene aldehyde (m/z 150), myrtenol (m/z 152), (2,2-dimethyl-3-acetyl)-cyclobutylformate (m/z 156), pinene acid (m/z 166), and isomers of pinalic-3-acid (m/z 170)), two additional nitrogen-containing species (i.e., C 10 hydroxy nitrate and C 10 carbonyl nitrate) were also observed at m/z values of 214 and 216 in the mass spectrum of βP-SOA. Furthermore, the losses of 18 (H 2 O), 46 (NO 2), and 64 (H 2 O + NO 2) were attributed to the typical fragmentation pathways of the two nitrogen-containing species. Overall, these results not only contribute to an improved understanding of βP-SOA formation, but they also indicate that TD-CH 2 Cl 2 -assisted LPPI-MS can be used as a novel detection means to study SOA formation. • Thermal desorption dichloromethane-assisted low-pressure photoionization mass spectrometry (TD-CH 2 Cl 2 -assisted LPPI-MS). • The photo-oxidation of β-Pinene was monitored with TD-CH 2 Cl 2 -assisted LPPI-MS. • Both non-nitrate organic and nitrate organic monomers were detected by TD-CH 2 Cl 2 -assisted LPPI-MS. [ABSTRACT FROM AUTHOR]

Oxidized organic molecules from ozonolysis of α-pinene are believed to participate in atmospheric new particle formation in forest regions. However, the detailed process of nucleation originated from α-pinene ozonolysis remains unclear. In this study, an atmospheric pressure interface time-of-flight mass spectrometer coupled with a planar differential mobility analyzer (DMA-MS) was applied to investigate the gas-phase reaction of α-pinene and ozone. Ion mobility and mass to charge ratio of the oxidized molecules were simultaneously measured. The ion mobility distribution of these oxidation products highlighted three mobility diameter ranges: 0.89–0.99 nm, 1.16–1.24 nm and 1.31–1.38 nm, where the dominating molecules were CH 2 O 2 , C 7-10 H 10-20 O 3-7 and C 19-20 H 30-32 O 6-9 , respectively. Combining the DMA-MS measurements, quantum chemistry calculations, and ion mobility modeling, the dominant monomer (C 10 H 16 O 3) was confirmed as pinonic acid while the primary dimer (C 20 H 32 O 6) was considered as pinonic acid cluster ((C 10 H 16 O 3) 2). Considering the yield of pinonic acid produced from α-pinene ozonolysis (2–4%), (C 10 H 16 O 3) 2 potentially accounts for part of the nocturnal C 20 dimers and ungrowable sub-2-nm particles in forests. Our work provides a new method to facilitate the understanding of atmospheric nucleation and initial growth. • A novel method to characterize molecular structures is introduced. • The dominating products of α-pinene ozonolysis are confirmed to be organic acid molecules and clusters. • Pinonic acid cluster potentially accounts for part of the nocturnal C 20 dimers and ungrowable sub-2-nm particles in forests. [ABSTRACT FROM AUTHOR]

The indoor air quality (IAQ) was investigated in 15 Passive Houses in the heating and non-heating seasons between 2019 and 2021 in Hungary. The concentrations of volatile organic compounds (VOCs), aldehydes, ozone, nitrogen dioxide, PM 2.5 mass, carbon dioxide, bacteria, fungi, and pollen were measured together with the monitoring of temperature, relative humidity and air change rate (ACR). The IAQ varied considerably among the investigated buildings. Significant seasonal differences were obtained for all physical parameters (temperature, relative humidity, ACR), certain VOCs (benzene, α-pinene, limonene), acetaldehyde, and airborne fungi. Considerable health concern was associated with the indoor concentrations of PM 2.5 mass and nitrogen dioxide in many cases based on the evaluation of IAQ in relation to potential adverse health effects, while the peak concentrations of other pollutants (e.g. trichloroethylene, α-pinene, certain aldehydes, fungi) were also of concern in a couple of cases. The median indoor/outdoor concentration ratios of benzene, PM 2.5 mass, nitrogen dioxide, ozone and fungi indicated that these pollutants are mainly of outdoor origin, while the other VOCs, aldehydes and bacteria showed higher concentration indoors. Overheating, the lack of proper particle filters in the mechanical ventilation system, and low ACR and relative humidity were identified as frequent problems related to the building characteristics. The emissions from building materials and furniture, the proximity of construction works and unpaved roads, and the allergenic vegetation might considerably influence IAQ. The results highlight that risk reduction measures are needed to create healthier indoor environment in the Passive Houses. • IAQ was measured in 15 Passive Houses in Hungary between 2019 and 2021. • Several IAQ parameters showed significant seasonal difference. • The highest health concern was on PM 2.5 and NO 2 concentrations in most cases. • Risk reduction measures are needed to create healthier IAQ in Passive Houses. • Air pollutants were present in similar concentrations compared to previous studies. [ABSTRACT FROM AUTHOR]

In this study, 13 secondary organic aerosol (SOA) tracers in PM 2.5 were measured in Jinzhong, Shanxi, to investigate the distribution characteristics of SOAs. According to the results, isoprene SOA tracers had the highest annual average concentration at 7.35 ± 14.23 ng/m3, accounting for 57.8% of all tracers by concentration, followed by β-caryophyllene SOA tracer (3.53 ± 2.67 ng/m3, 22.6%), α/β-pinene SOA tracers (2.68 ± 2.23 ng/m3, 18.9%) and toluene SOA tracer (0.11 ± 0.08 ng/m3, 0.7%). The concentrations of isoprene and α/β-pinene SOA tracers in summer and autumn were higher than those in winter and spring, whereas the concentration of β-caryophyllene SOA tracer was higher in autumn and winter than in spring and summer. However, no statistically significant seasonal variation was observed in the concentration of the toluene SOA tracer. According to results for pinolic acid and 3-methyl-1,2,3-butanetricarboxylic acid, α/β-pinene SOA tracers in Jinzhong were fresh in winter and the contribution ratio of β-pinene to SOA formation was higher than that of α-pinene. A correlation analysis also indicated that the high concentrations of isoprene and α/β-pinene SOA tracers in summer were correlated with temperature, whereas the high concentration of the β-caryophyllene SOA tracer in autumn and winter was primarily correlated with biomass burning. According to tracer yield estimation results, plant-derived volatile organic compounds were the main source of SOAs in PM 2.5 in Jinzhong, with a contribution ratio of 94%. Isoprene contributed the most to secondary organic carbon concentrations in spring and summer, whereas β-caryophyllene contributed the most in autumn and winter. • Distribution characteristics and seasonal variations of secondary organic aerosols in PM 2.5 in Jinzhong were investigated. • The factors influencing the concentration of secondary organic aerosols were discussed. • The contribution of isoprene to SOC was highest in spring and summer. • The contribution of β-caryophyllene to SOC was highest in Fall and Winter. [ABSTRACT FROM AUTHOR]

The molecular composition of secondary organic aerosol (SOA), obtained from the ozonolysis and photooxidation of α-pinene, was investigated using ultrahigh-resolution Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) in negative ion mode electrospray ionization (ESI). SOA formation was performed in an indoor smog chamber. The molecular formulae of individual species were identified on the basis of the measured ionic mass using guidelines, such as number of atoms, elemental ratios, and the nitrogen rule. In each of the SOAs obtained, 815–3501 monomeric and oligomeric (mainly dimeric) species were identified below m/z 800. From ozonolysis, mainly 95% of the typical oxygenated species (CHO) were detected, whereas from photooxidation under high NO x conditions, 32% of nitrogen-containing species (CHON) were detected. Several common intense species (e.g., C 9 H 14 O 6 , C 10 H 14 O 6 , C 10 H 16 O 5 , C 17 H 26 O 7 , C 19 H 28 O 9 , C 10 H 15 NO 8 , and C 10 H 15 NO 9 ) could be listed as candidate tracers for the conventional tracers for α-pinene SOA. The increased percentage of CHON as a primary effect of NO x on the SOA composition evidently affected other physicochemical parameters, such as elemental ratios (i.e., O/C, H/C, and N/C), the double-bond equivalent (DBE), the carbon oxidation state (OS C ), and the organic-mass-to-carbon ratio (OM/OC). The O/C and OM/OC for CHON were greater than those observed for CHO, indicating that nitrogen preferentially exists in the oxidized form (e.g., -ONO 2 ). The complexity of oligomerization was observed in DBE and OM/OC according to the number of carbon atoms. [ABSTRACT FROM AUTHOR]

This study presents detailed characterizations of a newly-developed flow reactor including (1) residence time distribution measurements, (2) relative humidity (RH) and temperature control, and (3) OH radical exposure range (i.e., atmospheric aging time). Hydroxyl (OH) radical exposures ranged from 8.20 × 10 10 to 7.22 × 10 11 molecules cm −3 s (0.5–4.9 d of atmospheric aging). In this study, the effects of NH 3 gas on the secondary organic aerosol (SOA) formation of α-pinene by dark ozonolysis and photooxidation were investigated using the newly-developed flow reactor. For both dark α-pinene ozonolysis and photooxidation, higher SOA yields were observed in the presence of NH 3 than in the absence of NH 3 . At RH of ∼50%, the SOA yield for ozonolysis and photooxidation in the presence of NH 3 increased by 23% and 15% relative to those in the absence of NH 3. Similar effects were observed at lower and higher RH conditions. Fourier transform infrared spectroscopy analysis confirmed the presence of nitrogen-containing functional groups in SOA formed in the presence of NH 3 . The α-pinene SOA formed in the presence of NH 3 showed higher absorption and fluorescence for UV-visible radiation than those formed in the absence of NH 3 . [ABSTRACT FROM AUTHOR]

Once pesticides are released into the environment, their active ingredient and other formulation compounds, such as coadjuvants or solvents, may undergo biological and chemical degradation, and form a range of products that could be even more hazardous than their precursors. These degradation products may also interact with the natural biogenic compounds emitted by treated crops, which leads to secondary air pollutants, such as ozone (O 3) or fine particulate matter, which directly affect human health and climate warming. This research provides evidence for the atmospheric process influencing the atmospheric and environmental fate of pesticides, active substance chloropicrin and commercially formulated chlorpyriphos, which interact with biogenic volatile organic compounds (α-pinene and a mixture of monoterpenes) simulating mixtures of terpenes emitted by orange trees at the large outdoor European PHOto-REactor (EUPHORE). Significant SOA formations were observed during the photolysis and/or ozonolysis of both pesticides in the presence of biogenic volatile organic compounds. For the photolysis of chloropicrin in the presence of α-pinene, the aerosol and O 3 formation yields ranged from 6 to 16% and 167–338%, respectively, depending on the initial conditions. For the photolysis of commercial chlorpyrifos in the presence of a mixture of terpenes, the formed aerosol yield was 24%, higher than those obtained by the photolysis of the terpenes in the absence of pesticides. Both pesticides in combination with terpenes increased O 3 formation. O 3 reacted with those terpenes, which increased particulate matter formation and may pose atmospheric issues on local and global scales. [Display omitted] • Atmospheric oxidation study of terpenes and chloropicrin and chlorpyrifos. • Pesticide degradation in the air leads to ozone and fine particle matter. • BVOCS photolysis or ozonolysis enhances SOA formation with pesticides present. • The plant protection products-BVOCs interaction produces high ozone and SOA levels. [ABSTRACT FROM AUTHOR]

Biogenic secondary organic aerosol (BSOA) in PM 2.5 over Bhopal, central India were quantified. Fine particles were collected on Teflon filters for measuring PM 2.5 mass and on quartz fiber filter for organic carbon (OC), elemental carbon (EC), and BSOA tracers, including oxidation products of isoprene, monoterpene and sesquiterpene between November 2017 and May 2018. Isoprene SOA tracers were present in the highest mean concentration (86.5 ng m−3 ± 93.5 ng m−3) amongst all quantified tracers, accounting for 64% ± 23% of the BSOA tracers. Isoprene oxidation products, including C 5 -alkene triols and 2-methyltetrols, and sesquiterpene oxidation products (β-caryophyllinic acid), were found to be the most abundant compound class over the study location. Correlations in the temporal variation of tracers of isoprene and monoterpene, with ozone (O 3) suggested that photochemical oxidation influenced their concentrations over central India. The temporal variation of β-caryophyllinic acid and comparison with the previous suggested that their concentration was potentially influenced by biomass burning. Overall, the findings suggest that oxidation products of isoprene, monoterpene and sesquiterpene can be utilized to understand the characteristics and apportionment of BSOA sources over central India. • BSOA tracers at a regional site in Central India were characterized. • Isoprene was the dominant contributor to SOA tracers. • Ratio of α/β-pinene tracers suggested that SOA were freshly formed. • Monoterpene SOA was predominantly produced by the oxidation of α-pinene. • BSOA was impacted by atmospheric oxidation and biomass burning. [ABSTRACT FROM AUTHOR]

In this study, the sorptive loss properties of biogenic volatile organic compounds (BVOCs) in polyester aluminum bags were investigated as a function of storage duration. To this end, the relative recovery of gas phase standards of BVOCs, obtained via vaporization of liquid phase standards, was computed by calibrating their standards (response factors: RF) represnting each phase. Accordingly, the results indicated either slight loss (−5.59% (isoprene), −2.39% (camphene), −1.69% ((R)-(+)-limonene), −0.88% ( p -cymene)) or gain (1.47% (γ-terpinene), 2.27% (α-terpinene), 2.63% (α-phellandrene), 2.73% ((+)-3-carene), 3.93% ((+)-β-pinene), and 5.98% ((+)-α-pinene)). Through comparison of the calibration results across storage time, the temporal stability of BVOCs was assessed. Longer BVOC storage time in polyester aluminum (PEA) bags lowered the relative recovery of BVOCs. The relative loss of BVOCs, if calculated in terms of mean bag standard RF ratios (relative to liquid standard) across elapsed time, decreased systematically: 0.99 ± 0.05 (0 h), 0.88 ± 0.06 (24 h), 0.66 ± 0.11 (72 h), and 0.62 ± 0.14 (120 h). It is thus recommended to complete the analysis of BVOC in PEA bags within 24 h of sample acquisition. As such, it is important to apply appropriate sampling approaches with a proper storage plan when measuring ambient BVOCs collected by bag sampling methods. [ABSTRACT FROM AUTHOR]

The hydroxyl radical oxidation of α -pinene under high NO x conditions was studied in a photochemical reaction chamber to investigate organic nitrate (RONO 2 ) production and fate between the gas and particle phases. We report an organic nitrate yield of 26 ± 7% from the oxidation of this monoterpene in the presence of nitric oxide (NO). However, the apparent organic nitrate yield was found to be highly dependent on both chamber relative humidity (RH) and seed aerosol acidity, likely as a result of particle phase hydrolysis. The particle phase loss of organic nitrates is believed to increase the gas to particle partitioning within the system, leading to decreased RONO 2 yields in both the gas and particle phases at elevated RH and an apparent non-equilibrium partitioning mechanism. The hydrolysis of particle phase organic nitrates in this study, starting at low chamber relative humidity, implies that aerosol partitioning of organic nitrates may be an important sink for atmospheric NO x and may have a significant impact on regional air quality. [ABSTRACT FROM AUTHOR]

Composition of the freshly formed secondary organic aerosol (SOA) generated by ozonolysis of cyclohexene, cyclohexene-d10 (model precursors) and α-pinene was studied using liquid chromatography coupled to electrospray ionization tandem mass spectrometry (LC-ESI/MS²). SOA was generated in the flow-tube reactor under the following conditions: 22 ± 2 °C, 1 atm and reaction time was approx. 30 s. In an attempt to resolve the current ambiguities, regarding the structure of α-pinene SOA nucleating agents, analytical methods for analysis of α-acyloxyhydroperoxy aldehydes and oligomers containing carboxylic group were developed to study the potential nucleating agents. Negatively charged m/z 351, 341, 337, 357 and 367 ions corresponding to the acidic oligomers were detected in freshly formed α-pinene SOA. For the first time, structures and formation mechanism for compounds detected as m/z 337 and 351 ions were proposed. Based on the model precursor analysis (cyclohexene and cyclohexene-d10) it was concluded that these compounds were most likely formed via aldol reaction of the lower molecular weight aerosol components. α-Acyloxyhydroperoxy aldehydes were studied in the SOA samples using previously developed, novel method, based on the prediction of fragmentation spectrum for the compounds of interest. It was concluded that α-acyloxyhydroperoxy aldehydes were not formed in significant quantities. Based on the obtained results, possible SOA formation and growth mechanism is discussed. [ABSTRACT FROM AUTHOR]

Mixing ratios and fluxes of volatile organic compounds (VOCs) were measured by PTR-MS (and GC-MS) and virtual disjunct eddy covariance during a three-week field campaign in summer 2009 within and above a Douglas fir (Pseudotsuga menziesii) forest in Speulderbos, the Netherlands. Measurements included the first non-terpenoid species fluxes and mixing ratios for Douglas fir canopy. Above-canopy emissions of monoterpenes were comparable to previous studies of P. menziesii, with estimated standard emission factors for the first and second halves of the campaign of 0.8 ± 0.4 and 0.8 ± 0.3 µg gdw-1 h-1, and temperature coefficients of 0.19 ± 0.06 and 0.08 ± 0.05 °C-1, respectively. Estimated isoprene standard emission factors for the two halves of the campaign were 0.09 ± 0.12 and 0.16 ± 0.18 µg gdw-1 h-1. Fluxes of several non-terpenoid VOCs were significant, with maximum fluxes greater than has been measured for other coniferous species. a-Pinene was the dominant monoterpene within and above the canopy. Within-canopy mixing ratios of individual species were generally greatest in early evening consistent with reduced vertical mixing and continued temperature-dependent emissions. Acetaldehyde, acetone and monoterpenes had elevated mixing ratios toward the bottom of the canopy (5-10 m) with assumed contribution from the large quantities of forest-floor leaf litter. MBO (2-methyl-3-buten-2-ol) and estragole had peak mixing ratios at the top of the canopy and are known to have coniferous sources. MVK + MACR (methyl vinyl ketone and methacrolein) also had highest mixing ratios at the top of the canopy consistent with formation from in-canopy oxidation of isoprene. The work highlights the importance of quantifying a wider variety of VOCs from biogenic sources than isoprene and monoterpenes. [ABSTRACT FROM AUTHOR]

Rate coefficient for the reaction of β-pinene with OH radicals was determined at 298 K and 800 Torr of N2 using the relative rate technique. Isobutylene was used as a reference compound and the concentrations of the organics were followed by gas chromatographic analysis. The rate coefficient for the reaction of β-pinene with OH radical was measured to be (9.35 ± 2.79) × 10−11 cm3 molecule−1 s−1. Theoretical kinetic calculations were also performed for the title reaction using canonical variational transition state theory (CVT) with small-curvature tunneling (SCT). The kinetics data obtained over the temperature range of 200–400 K were used to derive the Arrhenius expression: k(T) = 8.24 × 10−23 T 3.41 exp[2421/T] cm3 molecule−1 s−1. The OH-driven atmospheric lifetime (τ) and global warming potential (GWP) for β-pinene were computed and concluded that β-pinene is very short lived (2.5 h) in the Earth's atmosphere with a GWP of 1.6 × 10−2 at 20 years horizon of time and which is negligible. The ozone formation potential of β-pinene was also calculated and reported in this present work. [ABSTRACT FROM AUTHOR]

Abstract: Although it is a significant contributor to atmospheric particles, the role of mineral dust in secondary organic aerosol (SOA) formation has not been fully recognized. In this study, alumina was chosen as the surrogate to investigate the effect of mineral dust on α-pinene/NO x photo-oxidation in a 2 m3 smog chamber at 30 °C and 50% relative humidity (RH). Results showed that alumina seeds could influence both the SOA yield and the aerosol size in the photo-oxidation process. Compared to the seed-free system, the presence of alumina seeds resulted in a slight reduction of SOA yield, and also influenced the final concentration of O3 in the chamber. As an important oxidant of α-pinene, the decrease in O3 concentration could reduce the formation of semi-volatile compounds (SVOCs) and consequently inhibited SOA formation. In addition, the size of aerosol was closely related with the mass loading of alumina seeds. At low alumina concentration, SVOCs condensed onto the pre-existing seed surface and led to aerosol size growth. When alumina concentration exceeded about 5 μg m−3, SVOC species that condensed to each seed particle were dispersed by alumina seeds, resulting in the decrease in aerosol size. [Copyright &y& Elsevier]

Abstract: In the atmosphere, multiple volatile organic compounds (VOCs) co-exist, and they can be oxidized concurrently and generate secondary organic aerosol (SOA). In this work, SOA is formed by the oxidation (in presence of excess ozone) of mixtures containing α-pinene and other VOCs. The VOC mixtures were made so their composition approached a commercially-available α-pinene-based essential oil, Siberian fir needle oil. The SOA products were sampled using filters, solvent extracted and analyzed by gas chromatography/mass spectrometry with trimethylsilyl derivatization. The individual product yields for SOA generated from α-pinene changed upon the addition of other VOCs. An increase in concentration of non-reactive VOCs (bornyl acetate, camphene, and borneol) lead to a decrease in individual product yields of characteristic α-pinene SOA products. Although these experiments were carried out under higher VOC and ozone concentrations in comparison to the atmosphere, this work suggests that the role of non-reactive VOCs should be explored in SOA products formation. [Copyright &y& Elsevier]

Abstract: A set of experiments carried out at the EUPHORE smog chamber have been simulated using a simplified version of the Community Multiscale Air Qualtity model version 4.7 (CMAQv4.7). First, the terpene parameterizations included in the model have been tested against the experimental data, showing a general overprediction of the aerosol mass formed. Experimental differences between the experiments presented here and those from which the model parameters were obtained, such as the NO:NO2 ratio and the type of OH-initiator seem to be the reason of the overprediction observed. In the second part of the work, new parameterizations have been calculated for the two different set of conditions defined: CALTECH conditions, based on the experiments by and (low NO:NO2 ratio and propene as OH-inititator) and EUPHORE conditions, based on the experiments of this work (high NO:NO2 ratio and HONO as OH-initiator). We have estimated increases of 11% and 82% in the stoichiometric coefficients α i of the surrogate semivolatile products when the conditions change from EUPHORE to CALTECH conditions. Finally, the parameterizations are tested against an independent set of experiments published by . Results indicate that the parameters derived for the EUPHORE conditions simulate well experiments carried out under similar conditions. However, the parameters tend to overpredict SOA formation under high NOx conditions. [Copyright &y& Elsevier]

Abstract: Secondary organic aerosol (SOA) of α-pinene ozonolysis with and without hydroxyl radical scavenging hexane was characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Molecular formulas for more than 900 negative ions were identified over the mass range of 100–850u. Hydroxyl radicals formed during the ozonolysis of α-pinene might be expected to alter the composition of SOA, however a majority of the molecular formulas were identified in all three experiments and with a few exceptions they had similar relative abundances. Thus, the detailed composition of SOA was only slightly influenced by the presence or absence of hydroxyl radical scavenging hexane. The negative-ion mass spectra of the SOA contained four groups of peaks with increasing mass spectral complexity corresponding to increasing molecular weight. The mean values of O:C decreased from 0.55 to 0.42 with increasing molecular weight, but the mean value of H:C, approximately 1.5, did not change with increasing molecular weight. The molecular formulas with the highest relative abundances in Groups I and II contained 5–7 and 7–10 oxygen atoms and 3–4 and 5–7 double bond equivalents, respectively. The molecular formulas with the highest relative abundances in Groups III and IV contained 10–13 and 13–16 oxygen atoms and 7–9 and 9–11 double bond equivalents, respectively. Observations of the oxygen content and the double bond equivalents of the SOA products suggest a complex mixture of accretion reaction mechanisms, without an easily confirmable dominating pathway. [ABSTRACT FROM AUTHOR]

Abstract: Studies have demonstrated that cis-pinonic acid (CPA) is an important product from the oxidation of pinenes with ozone. CPA has been measured on aerosols and is used as an aging indicator for secondary organic aerosols (SOA). CPA levels and formation in urban aerosols and its annual variability, however, are still poorly understood. Here, we present monthly CPA average concentrations on aerosols in Toronto, Ontario, Canada based on a two-year-period: 2000–2001. They displayed a seasonal pattern associated with temperature and ozone (O3) plus nitrogen dioxide (NO2) reflecting the influence these have on emissions of pinenes from forests and their atmospheric oxidation, respectively. However, in Toronto some months with higher CPA concentrations, especially in the winter, were inconsistent with the seasonality of temperature or/and O3 + NO2 levels. Instead these deviations were associated with increases in wood burning tracers such as dehydroabietic acid (DHAA) and sugars. Similar features were observed during a two-week-period comparing day and nighttime CPA concentrations in the Lower Fraser Valley (LFV) of British Columbia, Canada, in that the CPA concentrations clearly varied diurnally with temperature and O3 + NO2 on some days, but also showed a significant correspondence with variations in the wood burning tracer concentrations, such as levoglucosan. These findings demonstrate that CPA formation is strongly impacted by wood burning activity. [Copyright &y& Elsevier]

Abstract: Simulations of the levels of organic particulate matter (OPM) in chemical transport models typically proceed by a two-product (2p) model approach, in which up to two lumped products are assumed to represent the condensable oxidation products of each hydrocarbon precursor. With the 2p approach, as well as with more detailed semi-explicit approaches, significant underpredictions of OPM levels are not uncommon, particularly at low OPM mass loadings in the atmosphere and in chamber studies. Here the recently developed np+mP OPM model approach was applied to evaluate OPM formation by α-pinene ozonolysis using: 1) product lumping based on carbon number and an estimate of molecular polarity, and 2) explicit inclusion of a low-volatility “polymeric” (P) compound. The np+mP approach allows for consideration of more than two products of type p (n > 2) per precursor, and consideration of further oxidation and/or reaction of those products to form m essentially non-volatile high molecular weight products of type P. Simulations were carried out for several different case types, namely 16p+0P, 8p+0P, 5p+0P, and 5p+1P in which one representative low-volatility compound was added. Predicted OPM levels were compared with levels predicted using alternative parameterizations (2p and volatility basis set) and with levels measured in chamber experiments conducted over a range of α-pinene oxidation conditions. The results from the 5p+1P case provided good agreement with available data from low, atmospherically-relevant mass loading experiments. Predicted O:C and H:C ratios also were compared with measured ratios, providing insight into differences and similarities between model compounds and the products they represent. The results will inform further development of OPM models, especially as regards oxidation product lumping and inclusion of low-volatility products. [Copyright &y& Elsevier]

Abstract: A method for measuring an aerosol light absorption coefficient (Ba ) has been developed using a conventional UV–visible spectrometer equipped with an integrating sphere covering a wide range of wavelengths (280–800 nm). The feasibility of the proposed method was evaluated in both the transmittance mode (TUV-IS) and the reflective mode (RUV-IS) using the reference aerosol known for the cross-sectional area. The aerosol was collected on a conventional filter and measured for Ba values. The resulting RUV-IS method was applied to measure light absorption of secondary organic aerosol (SOA). SOA was produced through photooxidation of different precursor hydrocarbons such as toluene, d-limonene and α-pinene in the presence of NOx (60–70 ppb) and inorganic seed aerosol using a 2-m3 indoor Teflon film chamber. Of the three precursor hydrocarbons, the Ba value of toluene SOA (0.574 m2 g−1 at 350 nm) was the highest compared with Ba values for α-pinene SOA (0.029 m2 g−1) and d-limonene SOA (0.038 m2 g−1). When d-limonene SOA or toluene SOA was internally mixed with neutral [(NH4)2SO4] or acidic inorganic seed (NH4HSO4:H2SO4 = 1:1 by mole), the SOA showed 2–3 times greater Ba values at 350 nm than the SOA with no seed. Aerosol aging with a light source for this study reduced Ba values of SOA (e.g., on average 10% for toluene SOA and 30% for d-limonene SOA within 4 h). Overall, weak absorption appeared for chamber-generated SOA over wavelengths ranging from 280 to 550 nm, which fall into the sunlight spectrum. [Copyright &y& Elsevier]

Abstract: Ozone reacts with indoor-emitted terpenoids to form secondary organic aerosol (SOA). Most SOA research has focused on ozone reactions with single terpenoids or with consumer products, and this paper reports the results from an investigation of SOA formation from ozone reactions with both single terpenoids and mixtures of d-limonene, α-pinene, and α-terpineol. Transient experiments were conducted at low (25 ppb) and high (100 ppb) initial concentrations of ozone. The three terpenoids were tested singly and in combinations in a manner that controlled for their different reaction rates with ozone. The SOA formation was assessed by examining the evolution in time of the resulting number size-distributions and estimates of the mass concentrations. The results suggest that at higher ozone and terpenoid concentrations, SOA number formation follows a linear trend as a function of the initial rate of reaction. This finding was valid for both single terpenoids and mixtures. Generally speaking, higher ozone and terpenoid concentrations also led to larger geometric mean diameters and smaller geometric standard deviations of fitted lognormal distributions of the formed SOA. By assuming a density, mass concentrations were also assessed and did not follow as consistent of a trend. At low ozone concentration conditions, reactions with only d-limonene yielded the largest number concentrations of any experiment, even more than experiments with mixtures containing d-limonene and much higher overall terpenoid concentrations. This finding was not seen for high ozone concentrations. These experiments demonstrate quantifiable trends for SOA forming reactions of ozone and mixtures, and this work provides a framework for expanding these results to more complex mixtures and consumer products. [Copyright &y& Elsevier]

Abstract: In-particle reactions and reactivity may play a role in aerosol aging as well as health effects associated with airborne particles. One of the main hypotheses for the species causing the observed health effects are reactive oxygen species including hydrogen peroxide (H2O2). Secondary organic aerosol (SOA), the focus of this study, comprises a major fraction of ambient fine mode particle mass. SOA were generated via dark ozonolysis of α-pinene and β-pinene, as well as photochemical oxidation of α-pinene, β-pinene, and toluene. SOA particles generate a considerable amount of H2O2 in the aqueous phase. For the same particle mass, α-pinene and β-pinene SOA have higher H2O2 generation ability than toluene SOA. H2O2 levels were sensitive to the pH of the particle extraction solutions, decreasing as the pH was increased. SOA samples aged for 20 h in room air lost a significant fraction of the H2O2 compared to fresh samples. The H2O2 is likely from decomposition or hydrolysis of hydroxyhydroperoxides, peroxic acids and related species for α- and β-pinene SOA, and from redox cycling of quinoid compounds for toluene SOA. This study provides the first quantitative measurement of H2O2 for a range of SOA particle types. [Copyright &y& Elsevier]

Abstract: The volatility of secondary organic aerosol (SOA) produced from the ozonolysis of α-pinene, β-pinene, and limonene, at low and intermediate RH, and at low and high NOx conditions was investigated using a thermodenuder (TD). More than 90% of the α-pinene and β-pinene SOA volume (for 200nm particles) and approximately 75% of the limonene SOA evaporated at 70°C for a centerline residence time of approximately 16s in the heated zone. Practically all the SOA in all systems evaporated at approximately 90°C. The relative humidity during the formation of SOA had a small effect on its volatility (changes in the evaporated fraction were less than 10%). NOx concentrations had a significant impact on the volatility of α-pinene and β-pinene SOA (reductions of the evaporated fraction by approximately 30%), but a negligible effect on the volatility of limonene SOA. High NOx levels resulted in more volatile SOA than low NOx conditions due to the presence of relatively volatile nitrate containing species at high NOx. The behavior of the SOA in the thermodenuder can be reproduced using an aerosol dynamics model based on the volatility basis-set approach and SOA yield parameters derived in previous smog chamber studies if appropriate values of the mass accommodation coefficient and heat of vaporization (ΔH vap) are chosen. Use of either a very low effective accommodation coefficient (0.002–0.01) and a heat of vaporization depending on the saturation concentration, or an effective accommodation coefficient of 0.05 for the initial stages of the evaporation and 1 afterward, with a low volatility-independent value of the ΔH vap, is needed for the simulation of the SOA evaporation. [Copyright &y& Elsevier]

Abstract: A series of experiments have been carried out in the York University smog chamber designed to study the products and pathways of the HO radical oxidation of β-pinene. Experiments on the oxidation of β-pinene and its most prominent oxidation product, pinaketone, by HO radicals with initial NO ranging from 0 to 2.5 ppm have been undertaken. An atmospheric pressure chemical ionization (API) mass spectrometer was operated for online, real-time identification and time profiling of the gas phase oxidation products. The formation of six organic nitrate products has been distinguished of which two have been assigned identifications, C10 dihydroxy nitrate (C10H17NO5) and nitrooxy-pinaketone (C9H13NO4). The real-time profiling and sensitivity to initial NO mixing ratio of each product has provided new insight into the β-pinene + HO radical oxidation mechanism. The distinguished products exhibited either no sensitivity or enhanced formations upon increasing the initial NO mixing ratio. The results also provide evidence supporting the formation of higher order organic nitrate products with formation pathways independent of pinaketone oxidation. [ABSTRACT FROM AUTHOR]

Abstract: BOREAM, a detailed model for the gas-phase oxidation of α-pinene and its subsequent formation of Secondary Organic Aerosol (SOA), is tested against a large set of SOA yield measurements obtained in dark ozonolysis experiments. For the majority of experiments, modelled SOA yields are found to agree with measured yields to within a factor 2. However, the comparisons point to a general underestimation of modelled SOA yields at high temperatures (above 30 °C), reaching an order of magnitude or more in the worst cases, whereas modelled SOA yields are often overestimated at lower temperature (by a factor of about 2). Comparisons of results obtained using four different vapour pressure prediction methods indicate a strong sensitivity to the choice of the method, although the overestimated temperature dependence of the yields is found in all cases. Accounting for non-ideality of the aerosol mixture (based on an adapted UNIFAC method) has significant effects, especially at low yields. Our simulations show that the formation of oligomers through the gas-phase reactions of Stabilised Criegee Intermediates (SCI) with other molecular organic products could increase the SOA yield significantly only at very low relative humidity (below 1%). Further tests show that the agreement between model and measurements is improved when the ozonolysis mechanism includes additional production of non-volatile compounds. [ABSTRACT FROM AUTHOR]

Abstract: Seasonal volatile organic compound emission data from loblolly pine (Pinus taeda) and Virginia pine (Pinus virginiana) were collected using branch enclosure techniques in Central North Carolina, USA. P. taeda monoterpene emission rates were at least ten times higher than oxygenated monoterpene and sesquiterpene emissions in all seasons. α-pinene and β-pinene were the most abundant emissions, while β-caryophyllene had the highest sesquiterpene emission rate from this species. β-phellandrene was the dominant compound emitted from P. virginiana, followed by the sesquiterpene β-caryophyllene. Sesquiterpene emissions from P. virginiana have not been reported in the literature previously. Summer sesquiterpene emissions from P. virginiana were nearly as high as monoterpene emissions, but were 4–12 times lower than monoterpene emissions in the other seasons. Oxygenated monoterpenes and 2-methyl-3-buten-2-ol were emitted at higher rates from P. taeda than from P. virginiana. Temperature response of the pinenes from P. taeda is similar to previously reported values used in emission models, while that for other compounds falls at the lower end of the previously reported range. Temperature response of all compounds from P. virginiana is in reasonable agreement with previously reported values from other pine species. There is evidence of light dependence of sesquiterpene emission after accounting for temperature response from both species. This effect is somewhat stronger in P. taeda. Bud break, needle expansion, and needle fall (and therefore wind events) seemed to increase monoterpene emission during non-summer seasons. In some instances springtime monoterpene emissions were higher than summertime emissions despite cooler temperatures. Emissions of individual compounds within monoterpene, oxygenated monoterpene, and sesquiterpene classes were highly correlated with each other. Compounds from different classes were much less correlated within each species. This is due to a varying temporal emission patterns for each BVOC class and suggests different production, storage, and emission controls for each. Analysis of enclosure blanks and diurnal patterns indicates that, despite precautions, disturbance due to the enclosure technique may still impact monoterpene emission rate estimates. This did not appear to affect sesquiterpene emissions. [Copyright &y& Elsevier]

Abstract: Monthly average ambient concentrations of more than eighty particle-phase organic compounds, as well as total organic carbon (OC) and elemental carbon (EC), were measured from March 2004 through February 2005 in five cities in the Midwestern United States. A multi-variant source apportionment receptor model, positive matrix factorization (PMF), was applied to explore the average source contributions to the five sampling sites using molecular markers for primary and secondary organic aerosols (POA, SOA). Using the molecular makers in the model, POA and SOA were estimated for each month at each site. Three POA factors were derived, which were dominated by primary molecular markers such as EC, hopanes, steranes, and polycyclic aromatic hydrocarbons (PAHs), and which represented the following POA sources: urban primary sources, mobile sources, and other combustion sources. The three POA sources accounted for 57% of total average ambient OC. Three factors, characterized by the presence of reaction products of isoprene, α-pinene and β-caryophyllene, and displaying distinct seasonal trends, were consistent with the characteristics of SOA. The SOA factors made up 43% of the total average measured OC. The PMF-derived results are in good agreement with estimated SOA concentrations obtained from SOA to tracer yield estimates obtained from smog chamber experiments. A linear regression comparing the smog chamber yield estimates and the PMF SOA contributions had a regression slope of 1.01±0.07 and an intercept of 0.19±0.10μgOCm−3 (adjusted R 2 of 0.763, n =58). [Copyright &y& Elsevier]

Abstract: The aqueous ozonolysis of α-pinene and β-pinene was conducted under simulated tropospheric conditions at different pHs and temperatures. Three kinds of products, peroxides, carbonyl compounds, and organic acids, were well characterized, and the detection of these products provides effective evidence for understanding the atmospheric aqueous reaction pathway. We have two interesting findings: (1) the unexpected formation of methacrolein (MACR), with a yield of ∼40%, in the α-pinene–O3 aqueous reaction indicates a potentially new SOA formation pathway, because MACR is one of the important precursors of SOA; and (2) the surprisingly high yields of H2O2, ∼60% for the α-pinene–O3 reaction and ∼100% for the β-pinene–O3 reaction, indicates that H2O2 can be a significant contributor to the origin and transformation of oxidants in the atmosphere, especially in the humid regions. Moreover, we have determined the rate constant for aqueous reaction between MACR and H2O2 in pH 2 to 7 and obtained its upper limit as 0.13 M L−1 s−1. A mechanism concerning the formation of the species mentioned above is proposed, and it differs from that in the gas-phase reaction. We suggest that water plays a key role in the mechanism, by participating in the reactions as a direct reactant and by removing the excess energy of intermediates formed in the reactions. [Copyright &y& Elsevier]

The present study aimed to investigate OH-reactivity change in the OH-initiated photo-oxidation of isoprene, α-pinene and m -xylene under high NO x conditions in the smog chamber at the National Institute for Environmental Studies, Japan. In all OH-initiated photo-oxidation experiments, first-generation oxidation products measured by Fourier-transform infrared spectroscopy (FTIR) could not fully explain the OH reactivity of the products measured by the laser photolysis/laser-induced fluorescence technique, and ∼20%, ∼40%, and ∼70% of OH reactivity attributed to these volatile organic compound (VOC) products, respectively, were missing. A master chemical mechanism (MCM) calculation demonstrated that the observed OH reactivity during photo-oxidation could be explained with secondary VOC products. It was found that vapor wall loss (VWL) and aerosol formation (AF) strongly affected the OH reactivity when the photochemical reaction was prolonged, i.e., multiple oxidations were involved. The MCM calculation showed that aromatics have almost twice the productivity of OH reactivity attributed to secondary VOC products, P s_VOC , compared with isoprene and α-pinene at the beginning of the period not affected by VWL/AF. The evaluation of the missing OH reactivity from O 3 oxidation and the sequential multiple oxidations of secondary products still involves an uncertainty that originates from an incomplete knowledge of VWL/AF, and thus, further investigation is required to understand OH-reactivity evolution in both chamber and ambient observations. The error in photolysis rate and possibly unconsidered reactions of secondary products, such as the pinonaldehyde case, also presents potential uncertainty in the OH reactivity prediction and thus requires evaluation. ● OH-reactivity budget in the isoprene, α-pinene and m-xylene oxidation with OH was investigated in high NO x conditions. ● Master Chemical Mechanism (MCM) calculations were compared with experiments. ● Secondary produced VOCs predicted by MCM model could explain the missing OH reactivity. ● The estimation error in MCM prediction became large when multiple oxidations were involved due to vapor wall loss and aerosol formation. [ABSTRACT FROM AUTHOR]

Abstract: The photooxidation of ∼1ppm α-pinene in the presence of increasing concentrations of NO2 was studied in a Teflon® chamber at 72–88% relative humidity and 296–304K. The loss of α-pinene and formation of gas-phase products were followed using proton-transfer reaction mass spectrometry (PTR-MS). Gas-phase reaction products (and their yields) include formaldehyde (5±1%), formic acid (2.5±1.4%), methanol (0.6±0.3%), acetaldehyde (3.9±1.7%), acetic acid (8.6±1.9%), acetone (12±3%), pinonaldehyde (22±6%), and pinene oxide (0.9±0.1%). There was evidence of organic nitrates; and small peaks were tentatively assigned to norpinonaldehyde, 4-oxopinonaldehyde, propanedial, 2,3-dioxobutanal and 3,5,6-trioxoheptanal or 3-hydroxymethyl-2,2-dimethylcyclobutylethanone. The formation and growth of new particles were followed using a scanning mobility particle sizer (SMPS), and their chemical composition and density probed using single particle mass spectrometry (SPLAT II). SPLAT II showed that the suspended SOA consisted of a complex mixture of organic nitrates and oxygenates having a density of 1.21±0.02gcm−3, 20% larger than often assumed in calculating SOA yields. Three-wavelength light scattering measurements were consistent with particles having a refractive index characteristic of organic compounds, but the data could not be well matched at all three wavelengths with a single refractive index. The effect of addition of cyclohexane or NO on particle formation showed that ozonolysis was the major mechanism of SOA formation in this system. However, unlike simple ozonolysis, organic nitrates are formed in both the gas and particle phases. Identifying and measuring specific organic nitrates in both the gas and particle phases in air may help to elucidate why SOA formation has been reported in field studies to be associated with polluted urban areas, yet the carbon in these particles is largely contemporary, i.e., non-fossil fuel carbon. [Copyright &y& Elsevier]

A framework is presented and evaluated for the parameterization of smog chamber results for use in atmospheric chemical transport models (CTMs). The parameterization uses an absorptive partitioning model to describe formation of secondary organic aerosol (SOA). The key points of the framework are (1) the ability to fit results from several types of chamber experiments; (2) the use of a basis set of surrogate compounds characterized by fixed effective saturation concentrations instead of the more commonly used variable saturation concentrations; (3) calculation of uncertainties of the estimated SOA aerosol mass fractions (AMF) outside of the fitted experimental range; and (4) determination of the best effective enthalpy to reproduced observed temperature sensitivity. The features of this data analysis and fitting framework are demonstrated using simulated data, and actual measurements from α-pinene ozonolysis experiments. Representation of SOA formation using as many as 8 surrogate compounds with fixed effective saturation concentrations is shown to be feasible and has advantages over simpler parameterizations. [Copyright &y& Elsevier]

We determined hourly emissions of isoprene, monoterpenes and sesquiterpenes from Siberian larch, one of the major tree species in Siberian forests. Summer volatile organic compounds (VOCs) emission from Siberian larch consisted mainly of monoterpenes (about 90%). The monoterpene emission spectrum remained constant during the measurement period, almost half was sabinene and other major monoterpenes were Δ 3-carene, β-and α-pinene. During spring and summer, about 10% of the VOCs were sesquiterpenes, mainly α-farnesene. The sesquiterpene emissions declined to 3% in the fall. Isoprene, 2-methyl-3-buten-2-ol (MBO) and 1,8-cineole contributed to less than 3% of the VOC emission during the whole period. The diurnal variation of the emissions could be explained using a temperature-dependent parameterization. Emission potentials normalized to 30°C were 5.2–21μggdw −1 h−1 (using β-value of 0.09°C−1) for monoterpenes and 0.4–1.8μggdw −1 h−1 (using β-value of 0.143°C−1, mean of determined values) for sesquiterpenes. Normalized monoterpene emission potentials were highest in late summer and elevated again in late fall. Sesquiterpene emission potentials were also highest in late summer, but decreased towards fall. [Copyright &y& Elsevier]

Samples of fine particulate organic matter were collected outside Durham, NC in the Duke Research Forest as part of the CELTIC study in July 2003. Particulate samples were collected on quartz filters using high volume air sampling equipment, and samples were analyzed for polar and non-polar organic species. Among compounds analyzed, oxidation products of α-pinene, namely pinic acid and pinonic acid, were identified in all samples. Pinic acid, being a dicarboxylic acid, has a low vapor pressure of the order of 10−8 Torr and is expected to contribute significantly to secondary organic aerosol (SOA) formation from the oxidation of α-pinene. Source contribution estimates from primary organic aerosol emissions were computed using the organic species as molecular markers with the chemical mass balance (CMB) model. The unapportioned organic carbon (OC) was determined as the difference between measured OC and OC apportioned to primary sources. This unapportioned OC was then correlated with pinic and pinonic acid to get a better understanding of the role of monoterpene oxidation products to form SOA. A reasonably good fit between pinic acid concentrations and unapportioned OC levels is indicative of the contribution of α-pinene oxidation products to SOA formation in ambient atmosphere. The results are significant considering the role of monoterpene emissions to global atmospheric chemistry. [Copyright &y& Elsevier]

We study theoretically the effect of oligomer formation on secondary organic aerosol (SOA) growth following ozonolysis of-pinene. Our goal is to show qualitatively, using a simplified condensational growth model, that the formation of involatile oligomers can induce the condensation growth of aerosols even if the secondary organic species formed in the oxidation reactions are rather volatile and therefore poorly condensable. The closed system studied consists of a single effective gas-phase oxidation product, and a seed aerosol population consisting of monodisperse ammonium sulphate particles. The oligomer formation is described as an effective dimerisation reaction between the monomers in the aerosol phase. By varying the dimerisation constant until our model results match the results from earlier smog-chamber studies, we are able to make order-of-magnitude estimations of the unknown dimerisation rates needed to induce the observed SOA growth. We also make model simulations using atmospheric-pinene and ozone concentrations, and find that the effective dimerisation rate inducing SOA growth in the atmosphere has to be considerably higher than that causing SOA growth in smog-chamber conditions. [Copyright &y& Elsevier]

The secondary organic aerosol (SOA) yield of a series of montoerpenes was investigated to determine the relative amounts of organic mass, which can be attributed to mass produced by heterogeneous acid-catalyzed reactions. Five monoterpenes (α-pinene, terpinolene, d-limonene, Δ 2-carene, β-pinene) were studied using a 2m3 indoor Teflon chamber and SOA was created in the presence of both acidic and neutral inorganic seed aerosol. The relative humidity was varied to create differing acidic seed environments. The heterogeneous aerosol production was influenced by the seed mass concentration, the acidity of the inorganic seed aerosol, and also molecular structure of the monoterpene ozonolysis products. This study also can be incorporated with our previously presented model of the kinetic expression for SOA mass production from heterogeneous acid-catalyzed reactions. [Copyright &y& Elsevier]

Chamber experiments were conducted to study the aerosol products from the ozonolysis of the major atmospheric monoterpenes; α-pinene, β-pinene and limonene. It was found that the α-pinend–O3 reaction produced mainly 2′. 2′-dimethyl-3′-acetyl cyclobutyl ethanal (pinonaldehyde), the β-pinene–O3 reaction, mainly 6,6-dimethyl-bicyclo [3.1.1] heptan-2-one and the limonene–O3 reaction, several unidentified products. These products were sought in forest aerosols and pinonaldehyde was detected in the atmosphere. [Copyright &y& Elsevier]

The gas-phase ozonolysis of α-pinene has been studied in a stopped-flow system at 295±2 K and 950 mbar of synthetic air as well as under flow conditions at 295±0.5 K and 1000 mbar of synthetic air. Gaseous products were analyzed using on-line GC-MS/FID and FT-IR measurements. The formation of new particles (dp⩾3 nm) was followed by means of a differential mobility particle sizer system and an ultra-fine condensation particle counter.First, the reaction of OH radicals with c-hexane was reinvestigated. Products were c-hexanol with a yield of 0.35±0.06 and c-hexanone with a yield of 0.53±0.06. The rate coefficients of the consecutive reaction of OH radicals with c-hexanol and c-hexanone of (2.7±0.4)×10−11 and (6.1±0.9)×10−12 cm3 molecule−1 s−1, respectively, were obtained. From the reaction of OH radicals with c-hexanol, a c-hexanone yield of 0.58±0.07 was observed. Using the c-hexane scavenger technique, an OH radical yield of 0.68±0.10 was measured for the reaction of O3 with α-pinene applicable for H2O concentrations of ∼1.5×1015 and 2.6×1017 molecule cm−3.The formation yield of pinonaldehyde was found to be strongly dependent on the experimental conditions. Generally, the pinonaldehyde yield decreased for increasing α-pinene conversion. In the presence of an OH radical scavenger, maximum pinonaldehyde yields were 0.42±0.05 and 0.32±0.04 for [H2O]∼1.5×1015 and 2.6×1017 molecule cm−3, respectively. Under the present conditions the pinonaldehyde formation cannot be described via the reaction of a Criegee intermediate with H2O. This finding is corroborated by measurements of the co-product H2O2. The formation yield of α-pinene oxide of 0.03±0.015 was unaffected by experimental conditions.Newly formed particles were measured for a relatively wide range of experimental conditions. Particle formation was only detectable for an α-pinene conversion above 3×1011 molecule cm−3. The results of the present study suggest that the formation of new particles from the pure O3+α-pinene reaction is unlikely under atmospheric conditions. [Copyright &y& Elsevier]

Biofiltration is cost-effective for the treatment of gases containing low concentrations of volatile organic compounds (<3 gm[sup -3]). However, conventional biofilters, based on compost and bacterial activity, face problems with the elimination of hydrophobic compounds. Besides that, biofilter operational stability is often hampered by acidification and drying out of the filter bed. To overcome these problems, biofilters with fungi on inert packing material have been developed. Fungi are more resistant to acid and dry conditions than bacteria, and it is hypothesised that the aerial mycelia of fungi, which are in direct contact with the gas, can take up hydrophobic compounds faster than flat aqueous bacterial biofilm surfaces. Alpha-pinene was chosen as a model compound. It is an odorous compound emitted by the wood processing industry. In 21 biofilter columns four different packing materials were tested: perlite, expanded clay granules, polyurethane foam cubes and compost. The filters were inoculated with forest soil and ventilated with gas containing alpha-pinene. Start up took 1-2 months and removal efficiencies of more than 90% were observed, but mostly ranged from 50% to 90% due to overloading. In the filters containing perlite, clay, polyurethane and compost volumetric removal capacities of, respectively, 24, 33, 38 and 24 g alpha-pinene m[sup -3] filter bed h[sup -1] were attained and the gas pressure drops in the 60 cm high filter beds measured at a superficial gas velocity of 35 m h[sup -1] were 70, 550, 180 and 250 Pa. The results indicate that it is possible to develop biofilters based on the action of fungi with higher elimination capacities for alpha-pinene as reported in literature for bacterial biofilters. The use of polyurethane foam cubes is preferred because of the low gas pressure drop in combination with a high volumetric elimination capacity. [ABSTRACT FROM AUTHOR]